Power control methods are often implemented within wireless communication systems to minimize transmission power while still maintaining a desired communication performance level.
In 3G systems, a nested loop structure having an outer loop and an inner loop is used to control transmit power. In the outer loop, a target of SINR (Signal to Interference and Noise Ratio), RSCP (Received Signal Code Power), SNR (Signal to Noise Ratio) or other metrics for the receiver is adjusted so that a configured or predetermined BLER (BLock Error Rate) target for data transmission can be met. In the inner loop, a measured value of a metric such as SIR, SINR etc. for a received signal is compared to the target value of the metric. A TPC (Transmit Power Control) command may then be generated for delivery to the transmitter based on the result of the comparison (e.g., indicating whether transmit power modifications are desirable).
In 4G systems, similarly, a predetermined or configured target of a metric such as SINR, RSCP, SNR or other metrics for each UE is used. There is a closed loop power control which adjusts the transmission power of the UE with the generated TPC command by comparing the predetermined or configured target and the measured value of the metric.
It can be seen that according to existing power control methods, the power control command is generated based on the target value and the measured value of a certain metric without considering the measurement or estimation error of the metric. However, as observed in field tests of an uplink power control, for example, the UE performance is seriously deteriorated when there is a large measurement error of a metric usable to generate power control command, which is undesirable.